As revealed on Flyertalk, United Mileage Plus members booking business class transatlantic or transpacific award flights can only be booked in coach on Singapore connecting segments.

S*MPI/STAR-AWARD RULES.R:

**NOTE: X/I/O IS NOT OFFERED ON ALL ROUTES.

FOR SQ BUSINESS CLASS AWARDS WITH CONNECTIONS/STOPOVERS

TO/FROM A TRANSOCEANIC FLIGHT BOOK *I* CLASS FOR TRANSOCEANIC

FLIGHT ACROSS THE ATLANTIC/PACIFIC AND *X* FOR ONWARD FLT

EXAMPLE – SQ BUSINESS CLASS AWARD LAXDPS

BOOK *I* LAX-SIN AND *X* SIN-DPS

SQ AWARDS THAT DO NOT INVOLVE A TRANSOCEANIC

SECTOR USE *I* FOR ALL SECTORS INCLUDING 2 CABIN AIRCRAFT

Lesson is that if you fly Singapore on a business award you’ll want your onward connection on another Star carrier in order to remain in business.